Two bodies attract each other directly as the product of their masses and inversely as the square of their distance.' It sounds like a rule for simple physical facts, does it not? Yet it is nothing of the sort; it was the poetical way the old ones had of expressing the rule of propinquity which governs the emotion of love. The bodies referred to are human bodies, mass is their capacity for love. Young people have a greater capacity for love than the elderly; when thy are thrown together they fall in love, yet when they are separated they soon get over it. 'Out of sight, out of mind.' It's as simple as that. But you were seeking some deep meaning for it.

In 1934 he worked actively for the Democratic campaign of Upton Sinclair for Governor of California. F. He also examined the relationship between physical and emotional love explored various unorthodox family structures and speculated on the influence of space travel on human cultural practices.

In his fiction Heinlein coined words that have become part of the English language including "grok" and "waldo" and popularized the terms "TANSTAAFL" and space marine. Heinlein was named the first Science Fiction Writers Grand Master in 1974. He also examined the relationship between physical and emotional love explored various unorthodox family structures and speculated on the influence of space travel on human cultural practices.